1. Field of the Invention
This invention is related generally to an apparatus and method for grinding a backside surface of an integrated circuit wafer and, more particularly, to an apparatus and method for grinding a backside surface of an integrated circuit wafer that includes use of a cushioned grinding table and an organic acid cooling fluid.
2. Discussion of the Related Art
In a typical integrated circuit manufacturing process, a plurality of integrated circuit chips are simultaneously patterned and defined on a frontside surface of a single silicon wafer by a series of layer deposition and etching processes well understood in the art. The individual integrated circuit chips are generally patterned in a series of rows and columns in a rectangular format on the wafer. After the integrated circuit chips are fully defined, the wafer is then diced by a suitable sawing machine along lines between the rows and columns of the integrated circuit pattern to separate the wafer into the individual circuits. The individual integrated circuit chips can then be secured within protective packages and incorporated into appropriate electronic circuits.
U.S. patent application Ser. No. 08/249,815 filed May 26, 1994, titled "Method of Preventing Aluminum Bond Pad Corrosion During Dicing of Integrated Circuit Wafers," assigned to the assignee of the instant application and herein incorporated by reference, discloses a method of preventing metal bond pad corrosion and contamination during dicing of integrated circuit wafers. This method incorporates use of an organic acid cooling fluid that cools a saw blade of the sawing machine during dicing. The pH level of the cooling fluid established by the organic acid prevents silicon residue and particulates released from the wafer during the sawing process from adhering to metallic bond pads of the individual integrated circuit chips, and thus allows the silicon particulates to be washed away from the wafer with the cooling fluid.
Generally, the original silicon wafer on which the integrated circuits are patterned is sliced from a larger silicon crystal ingot. The silicon wafers,are sliced from the crystal ingot to a thickness that is greater than desirable for a finished integrated circuit product so as to provide a more robust wafer to stand up to the rigors of the integrated circuit fabrication processes. Particularly, relatively thick silicon wafers are necessary during the integrated circuit fabrication steps to prevent warpage and breakage of the wafer as a result of certain heating processes, as well as other circuit fabrication processes. However, the thickness of the wafer after the integrated circuits are fabricated is thicker than desirable for device packaging restrictions. Therefore, it is necessary after the integrated circuit patterns are defined to grind a backside surface of the wafer opposite to the frontside surface of the wafer where the integrated circuits are formed to reduce the wafer thickness prior to the wafer being diced to separate the wafer into the individual integrated circuit chips. Suitable grinding machines are well known in the art that are capable of grinding down the backside surface of the silicon wafer. Known types of grinding machines generally include a plurality of chuck tables that secure a plurality of wafers to be ground by one or more grinding wheels.
The current industry standard is to apply either a spin-on coating of a resist material, or other applicable material, or a dry film tape to the frontside of the finished integrated circuit chip wafer to cover and protect the integrated circuits during the backside grinding process. The frontside protective cover of the integrated circuit chip wafer prevents silicon residue contaminants from adhering to the metallic bond pads of the integrated circuits during grinding. Once the grinding process is complete, the spin-on coating is etched away in a wet bath, or an applicable machine is used to remove the dry film tape.
Although the spin-on coating or dry film tape has effectively prevented silicon residue from contaminating the bond pads during grinding, removal of the spin-on coating or dry film tape has resulted in contamination of the integrated chips by residue from the coating or tape. This contamination can cause integrated circuit device failures or poor test yields. Also, the chuck table applies pressure to the frontside surface of the silicon wafers where the integrated circuit chips are formed to hold the wafer in place. This pressure sometimes causes damage to the integrated circuit chips because epitaxial spikes or foreign material are formed during device layer deposition. Although the spin-on coating or dry film tape provides some cushioning against damage of this nature, the thickness of the coating or tape is not enough to protect the integrated circuit chips against many epitaxial spikes and other foreign material commonly present from integrated circuit fabrication.
What is needed is a method and associated apparatus that allows grinding of a backside surface of a silicon wafer that does not cause pressure damage to the integrated circuit chips on a frontside surface of the wafer, and does not allow contamination of the integrated circuit chips and associated metallic bond pads during the grinding process. It is therefore an object of the present invention to provide such an apparatus and process.